Method for the production of alpha-alane

ABSTRACT

A method of forming alpha-alane. The method includes reacting aluminum trichloride and an alkali metal hydride to form an alane-ether complex solution. An aqueous ether solution is optionally added to the alane-ether complex solution to form a partially hydrolyzed ether/alane-ether complex solution. A solution of a crystallization additive is added to the alane-ether complex solution or to the aqueous ether/alane-ether complex solution to form a crystallization solution. The crystallization additive is selected from the group consisting of squalene, cyclododecatriene, norbomylene, norbomadiene, a phenyl terminated polybutadiene, 2,4-dimethyl anisole, 3,5-dimethyl anisole, 2,6-dimethyl anisole, polydimethyl siloxane, and mixtures thereof. Ether is removed from the crystallization solution to crystallize the alpha-alane.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional PatentApplication Ser. No. 60/559,588, filed Apr. 5, 2004, for METHOD FOR THESYNTHESIS OF α-ALANE.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH

The U.S. Government has a paid-up license in this invention and theright in limited circumstances to require the patent owner to licenseothers on reasonable terms as provided for by the terms of Contract No.N00014-02-C-0282.

FIELD OF THE INVENTION

The present invention relates to a method of producing alane. Morespecifically, the present invention relates to a method of producing analpha polymorph of the alane that utilizes a crystallization additiveand, optionally, water, but that does not use borohydride salts.

BACKGROUND OF THE INVENTION

Aluminum hydride (“AlH₃”) or alane is formed as numerous polymorphs: thealpha (“α”), alpha prime (“α′”), beta (“β”), delta (“δ”), epsilon (“ε”),zeta (“ζ”), or gamma (“γ”) polymorphs. Each of the polymorphs hasdifferent physical properties and varying stability. As disclosed inU.S. Pat. No. 6,228,338 to Petrie et al. (“Petrie”) and Brower et al.(“Brower”), “Preparation and Properties of Aluminum Hydride,” J. Am.Chem. Soc., 98(9):2450-2453 (1976), α-alane is the most thermally stablepolymorph and its crystals have a cubic or rhombohedral morphology. Incontrast, α′-alane forms needlelike crystals and γ-alane forms a bundleof fused needles. γ-alane is produced with the β polymorph, both ofwhich convert to α-alane upon heating. δ-alane and ε-alane are formedwhen trace amounts of water are present during crystallization. ζ-alaneis prepared by crystallization from di-n-propyl ether. The α′, δ, ε, andζ polymorphs do not convert to α-alane and are less thermally stablethan α-alane. Therefore, the α′, δ, ε, and ζ polymorphs are typicallynot used in explosive or pyrotechnic compositions.

Alane includes about 10% hydrogen by weight and has a higher density ofhydrogen than liquid hydrogen. Due to the high hydrogen density andhighly exothermic combustion of aluminum and hydrogen, alane is commonlyused as a fuel for propellants or as an explosive. When used in apropellant, the alane provides an increased specific impulse compared topropellants that use aluminum alone.

As disclosed in Petrie and Brower, α-alane is typically synthesized byreacting aluminum trichloride (“AlCl₃”) and lithium aluminum hydride(“LAH”) in diethyl ether. The aluminum trichloride is dissolved indiethyl ether at −10°C. A minimum of three mole equivalents of LAH isadded to the aluminum trichloride solution to produce a solvatedalane-ether complex and a precipitate of lithium chloride (“LiCl”). Todesolvate the alane-ether complex, 0.5-4 mole equivalents of aborohydride salt, such as lithium borohydride or sodium borohydride, ismixed with the solution including the alane-ether complex. The mixtureis filtered and the filtrate is diluted with toluene or benzene toprovide an ether to toluene or benzene ratio of 15:85. The mixture isheated to 85° C.-95° C. to desolvate the alane-ether complex and thediethyl ether is subsequently removed by distillation. The precipitatedalane is recovered by aqueous acid quenching, filtration, and washing.Brower also discloses that the reaction is conducted in the absence ofwater, oxygen, and other reactive species because if water is present,the δ and ε polymorphs are undesirably formed.

However, the borohydride salts used to desolvate the alane-ether complexare expensive and are not recovered, making this synthesis of α-alaneexpensive. The borohydride salts also generate byproducts that requiredisposal. Furthermore, the alane produced by the method of Petrie orBrower is typically contaminated with undesirable polymorphs and isprone to decomposition during heating. More importantly, since theα-alane is contaminated with the other alane polymorphs, this method ofproducing α-alane gives variable and irreproducible results.

Alane may also be synthesized from aluminum and hydrogen at a highpressure (0.5-6.5 GPa) and temperature (100° C.-700° C.), as disclosedin Konovalov et al., “High Pressures in the Chemistry of Beryllium andAluminum Hydrides,” Russian J. Inorg. Chem., 37(12):1361-1365 (1992).However, preparative quantities of the alane are not produced by thissynthesis due to the difficulty of creating gas holders for thehydrogen.

It would be desirable to reproducibly produce a high yield of α-alaneusing a low-cost synthetic method.

BRIEF SUMMARY OF THE INVENTION

The present invention relates to a method of producing α-alane. Themethod comprises reacting aluminum trichloride and an alkali metalhydride to form an alane-ether complex solution. The aluminumtrichloride and the alkali metal hydride may be reacted in diethyl etheror in a mixed solvent system comprising greater than approximately 50%diethyl ether. An aqueous ether solution is added to the alane-ethercomplex solution to form a partially hydrolyzed ether/alane-ethercomplex solution. The aqueous ether solution may include fromapproximately 0.5% by volume to approximately 4% by volume of water. Thepartially hydrolyzed ether/alane-ether complex solution is combined witha solution that comprises at least one crystallization additive to forma crystallization solution. The crystallization additive may be selectedfrom the group consisting of squalene, cyclododecatriene, norbomylene,norbomadiene, a phenyl terminated polybutadiene, 2,4-dimethyl anisole,3,5-dimethyl anisole, 2,6-dimethyl anisole, polydimethyl siloxane, andmixtures thereof. The crystallization solution is formulated to besubstantially free of an alkali metal borohydride.

The α-alane is crystallized from the crystallization solution byremoving ether from the crystallization solution. The ether may beremoved by heating the crystallization solution to a temperature rangingfrom approximately 80° C. to approximately 87° C. to reduce a volume ofether in the crystallization solution to less than approximately 10% byvolume. Additional ether may be added to the crystallization solutionand heated to a temperature ranging from approximately 88° C. toapproximately 95° C. to produce the α-alane. The α-alane may be exposedto an acidic solution comprising from approximately 10% by volume toapproximately 12% by volume of hydrochloric acid (“HCl”) to removeimpurities. The α-alane is produced without using alkali metalborohydride salts.

The present invention also relates to a method of producing α-alane thatcomprises reacting aluminum trichloride and an alkali metal hydride toform an alane-ether complex solution. The alane-ether complex solutionis combined with a solution that comprises at least one crystallizationadditive to form a crystallization solution. The at least onecrystallization additive is selected from the group consisting ofsqualene, cyclododecatriene, norbomylene, norbomadiene, polydimethylsiloxane, and mixtures thereof. α-alane is crystallized from thecrystallization solution.

DETAILED DESCRIPTION OF THE INVENTION

A method of producing α-alane is disclosed. The α-alane may besynthesized and crystallized without using borohydride salts, such aslithium borohydride or sodium borohydride. At least one crystallizationadditive may be utilized in producing the α-alane. In addition, watermay optionally be used to produce the α-alane. The alane produced by themethod of the present invention may be substantially the α polymorph andmay be produced in a high yield. As such, the α-alane has good stabilityand is unreactive to hydrolysis. As used herein, the term “alane” refersto AlH₃ and includes combinations of the different alane polymorphs. Incontrast, when referring to a specific polymorph of the alane, thedesignation of the specific polymorph is used, such as “α-alane” or the“a polymorph.”

To synthesize the alane, aluminum trichloride and an alkali metalhydride may be reacted in solution to produce an alane-ether complex(“AlH₃.Et₂O”) and an alkali metal chloride. As used herein, the term“alane-ether complex” refers to an etherate or ether adduct of thealane. The aluminum trichloride and the alkali metal hydride may bereacted in a first organic solvent in which both the aluminumtrichloride and the alkali metal hydride are soluble. The first organicsolvent may be an aliphatic ether, such as diethyl ether (“ether”),di-n-propyl ether, di-n-butyl ether, methyl-butyl ether, methyl-t-butylether, or mixtures thereof. Mixed solvent systems, such as a mixture ofdiethyl ether and toluene, may also be used as the first organicsolvent. The reaction of the aluminum trichloride and the alkali metalhydride may be conducted at a temperature of less than approximately 10°C., such as from approximately −5° C. to approximately −15° C.

The alkali metal hydride may be lithium hydride, sodium hydride,potassium hydride, calcium hydride, magnesium hydride, LAH, sodiumaluminum hydride, and mixtures thereof. In one embodiment, the alkalimetal hydride is LAH and the alkali metal chloride formed by thereaction is lithium chloride, as shown in Equation 1:3LiAlH₄+AlCl₃→4AlH₃.Et₂O+3LiCl  (Equation 1).The reaction may also proceed through a chloroalane intermediate, suchas AlHCl₂ or AlH₂Cl, which is reacted with additional amounts of thealkali metal hydride to form the alane-ether complex. To reactsubstantially all of the aluminum trichloride with the alkali metalhydride to produce the alane-ether complex, the alkali metal hydride maybe present in excess. For instance, the alkali metal hydride may bepresent, relative to the aluminum trichloride, in a molar ratio rangingfrom approximately 3:1 to approximately 5:1. The alkali metal chloride,which is lithium chloride in the embodiment shown in Equation 1,precipitates and may be filtered from the alane-ether complex solution,leaving the alane-ether complex dissolved or suspended in the firstorganic solvent. As shown in Equation 2 and described in detail below,the ether in the alane-ether complex solution may be removed to producethe α polymorph:AlH₃.Et₂O→α-AlH₃+Et₂O  (Equation 2).The resulting α-alane is polymeric and its crystals have a cubic orrhombohedral appearance.

After reacting the aluminum trichloride and the alkali metal hydride, anaqueous ether solution may optionally be added to the alane-ethercomplex solution to form a partially hydrolyzed ether/alane-ethercomplex solution. The water in the aqueous ether solution is believed toresult in partial hydrolysis of the alane-ether complex, resulting inthe formation of polymeric aluminum-oxo-hydrido species (e.g.(AlH_(3-n)O_(n))_(x), where x>1). The aqueous ether solution may be asolution of diethyl ether that is saturated with water. The aqueousether solution may include from approximately 0.5% by volume toapproximately 4% by volume of water. As such, the water may be presentin the alane-ether complex solution at less than approximately 0.1equivalent based on the aluminum. A total amount of water added to thealane-ether complex solution may range from approximately 0.1 mole % toapproximately 10 mole % of the alane present as the alane-ether complex.The small amount of water added to the alane-ether complex solution mayimprove product quality and reproducibility of the synthesis. Inaddition to providing the water in the aqueous ether solution, theappropriate amount of water may be introduced by adding a hydrated salt,such as hydrated sodium sulfate, to the alane-ether complex solution.The partially hydrolyzed ether/alane-ether complex solution may befiltered to remove any particulates, forming a solution or suspension ofthe alane-ether complex in the ether.

Before crystallizing the α polymorph, the partially hydrolyzedether/alane-ether complex solution may be diluted into a second organicsolvent, such as toluene, mesitylene, or xylene, to provide maximumsolubility for the alane. Alternatively, paraffinic hydrocarbons, suchas cyclohexane, heptane, cyclopentane, or mixtures thereof, may be usedas the second organic solvent. If the aqueous ether solution is notused, the alane-ether complex solution may be diluted into the secondorganic solvent. In one embodiment, the second organic solvent istoluene. A crystallization additive may be present in the second organicsolvent from approximately 0.05% by weight (“wt %”) to approximately 5wt %. The crystallization additive may be an aprotic, electron-richmaterial that is soluble in the second organic solvent. For instance,the crystallization additive may be an olefin, a polyolefin, an anisole,a polydimethyl siloxane, a tertiary amine, an aliphatic or aromaticether, or mixtures thereof. The olefin may include, but is not limitedto, squalene, cyclododecatriene, norbomylene, norbornadiene, a phenylterminated polybutadiene, and mixtures thereof. The anisole may include,but is not limited to, 2,4-dimethyl anisole, 3,5-dimethyl anisole,2,6-dimethyl anisole, and mixtures thereof. These compounds arecommercially available from various manufacturers, such as fromSigma-Aldrich Co. (St. Louis, Mo.). In one embodiment, thecrystallization additive is polydimethyl siloxane. The crystallizationadditive, which is in solution in the second organic solvent, may beused to form a crystallization solution that includes the partiallyhydrolyzed ether/alane-ether complex solution. Alternatively, thecrystallization solution may be formed by adding the crystallizationadditive to the partially hydrolyzed ether/alane-ether complex solution.

Seed crystals of α-alane may optionally be added during thecrystallization to promote the growth of the α-alane. The seed crystalsmay subsequently be incorporated into the α-alane.

To desolvate and crystallize the α polymorph, the ether may be removedfrom the crystallization solution, such as by distilling the ether. Toremove the ether, the crystallization solution may be heated at ambientor reduced pressure. For instance, if the ether is removed under vacuum,the crystallization solution may be heated at a temperature ranging fromapproximately 50° C. to approximately 60° C. However, if the ether isremoved at ambient pressure, a temperature ranging from approximately80° C. to approximately 100° C., such as from approximately 80° C. toapproximately 97° C., may be used. A rate at which the ether is removedmay affect the formation of the α-alane. If the ether is removed tooquickly, the alane-ether complex may precipitate from thecrystallization solution rather than forming the crystals of theα-alane. However, if the ether is removed too slowly, thecrystallization process may be too long for practical and economicalpurposes. In one embodiment, the ether is removed by heating thecrystallization solution to a temperature ranging from approximately 80°C. to approximately 95° C.

Multiple heating cycles and subsequent dilutions with additional ethermay be used to crystallize the α polymorph. The amount of ether in thecrystallization solution may initially be reduced to less thanapproximately 10% by volume by heating the crystallization solution to atemperature ranging from approximately 80° C. to approximately 87° C.,such as from approximately 82° C. to approximately 85° C. The remainingvolume of the crystallization solution may then be heated until aprecipitate is formed.

At an initial point in the distillation, spherical particles of thealane-ether complex may be present. It is believed that these sphericalparticles are not crystals but are crystalline. However, as the ether isdistilled, crystals of the alane may begin to form. The crystals formedinitially may have a needlelike morphology, indicating formation of theα′ polymorph. After the α′ polymorph forms, additional ether may beadded to the growing crystals. The additional ether may be removed byheating to a temperature ranging from approximately 88° C. toapproximately 95° C., such as from approximately 88° C. to approximately92° C. After removing the additional ether, the crystals may have acubic or rhombohedral appearance, indicating formation of the αpolymorph. Without being bound to a particular theory, it is believedthat the α′ polymorph crystals may transform to crystals of the αpolymorph upon heating and during distillation of the ether. Theformation of the different morphologies of the crystals may be observedby visual microscopy, such as by scanning electron microscopy (“SEM”) oroptical microscopy.

After substantially all of the ether has been removed, the crystals maybe filtered to remove any remaining toluene and seed crystals that maybe present, leaving the crystals of α-alane wetted with ether andtoluene. The α-alane crystals may be washed with an aqueous acidicsolution to remove any impurities, such as at least one of aluminum(formed by pyrolysis), the α′ polymorph, lithium chloride, LAH, andother undesirable polymorphs. The acidic solution may include fromapproximately 1% by volume to approximately 25% by volume of an acid,such as HCl, hydrofluoric acid, hydrobromic acid, phosphoric acid,perchloric acid, sulfuric acid, boric acid, or mixtures thereof. In oneembodiment, the acidic solution includes from approximately 10% byvolume to approximately 12% by volume of HCl. The crystals of theα-alane may then be filtered to remove the acidic solution. The α-alanecrystals may be rinsed with water to remove remaining trace amounts ofthe acidic solution, followed by rinses with acetone or isopropanol toremove the water. The α-alane crystals may then be dried.

Without being bound to a particular theory, it is believed that the αpolymorph nucleates and forms by conversion of the α′ polymorph oranother needlelike polymorph. However, the presence of needlelikepolymorphs during the crystallization is not a necessary or sufficientcondition for formation of the α polymorph. The crystallization additivemay also promote growth of the α polymorph by providing a nucleationsite for the α polymorph. The crystallization additive may also suppressformation of the undesirable polymorphs. It is also believed that earlyprecipitation of the crystals may promote the growth of the α polymorph.

The α-alane produced by the method of the present invention may includean amount of carbon that ranges from approximately 0.15% to less thanapproximately 1%, such as from approximately 0.15% to approximately0.25%. The amount of hydrogen in the α-alane may range fromapproximately 9.5% to approximately 10.2%, such as from approximately9.9% to approximately 10.1%. Trace amounts of nitrogen may also bepresent. The α-alane produced by the method of the present invention mayhave a particle (crystallite) size ranging from approximately 5 micronsto approximately 100 microns. The α-alane may have a density at roomtemperature that ranges from approximately 1.47 g/cc to approximately1.49 g/cc. The α-alane may also be substantially free of trace elements,such as chloride ions. For instance, the chloride ions may be present inthe α-alane in an amount of less than approximately 0.05wt %. Theα-alane may be substantially free of other alane polymorphs, such ashaving greater than or equal to approximately 90% of the α polymorph. Ahigh yield of the α-alane may also be achieved. The yield of α-alaneobtained by the method of the present invention may range fromapproximately 20% to approximately 60% based on the aluminum chloride,such as from approximately 50% to approximately 60% based on thealuminum chloride.

Since borohydride salts are not used, the method of the presentinvention provides a low-cost, high-performing method of producingα-alane. The method also produces a high yield of α-alane that issubstantially free of other polymorphs. As such, the α-alane may be ofimproved quality and may be reproducibly synthesized.

The α-alane may be used to formulate energetic materials, such asexplosive compositions, propellant compositions, or pyrotechniccompositions. In addition to using the α-alane as a fuel, the energeticmaterial may include at least one of a binder, an oxidizer, and anadditional fuel. The binder may be a conventional binder or fillermaterial including, but not limited to, a polyoxetane, a polyglycidylazide, a polybutadiene, a polybutadieneacrylonitrileacrylic acidterpolymer, a polyether, a polyglycidyl nitrate, a polycaprolactone, ormixtures thereof. Energetic or non-energetic polymers may also be used.Examples of the energetic or non-energetic polymers include, but are notlimited to, a cellulosic polymer, such as cellulose acetate butyrate(“CAB”) or nitrocellulose, a nylon, a polyester, a fluoropolymer, anenergetic oxetane, a wax, and copolymers thereof. The oxidizer mayinclude, but is not limited to, trinitrotoluene (“TNT”),cyclo-1,3,5-trimethylene-2,4,6-trinitramine (“RDX”), cyclotetramethylenetetranitramine (“HMX”), hexanitrohexaazaisowurtzitane (“CL-20”),4,10-dinitro-2,6,8,12-tetraoxa-4,10-diazatetracyclo-[5.5.0.0^(5,9).0^(3,11)]-dodecane (“TEX”), 1,3,3-trinitroazetine (“TNAZ”),ammonium perchlorate (“AP”), potassium perchlorate (“KP”), ammoniumdinitramide (“AND”), potassium dinitramide (“KDN”), sodium peroxide(“Na₂O₂”), sodium nitrate (“SN”), potassium nitrate (“KN”), ammoniumnitrate (“AN”), 2,4,6-trinitro-1,3,5-benzenetriamine (“TATB”),dinitrotoluene (“DNT”); and mixtures thereof. The additional fuel may bea metallic fuel, such as aluminum, beryllium, boron, magnesium,zirconium, mixtures thereof, or alloys thereof. The energetic materialmay also include other conventional ingredients, such as at least one ofa plasticizer, a burn rate modifier, and a ballistic additive.

The α-alane may also be used for hydrogen storage, such as providing ahydrogen source in fuel cells or batteries. The α-alane may beformulated into a composition that provides a controlled release ofhydrogen in the fuel cell or battery.

The α-alane may also be used as a chemical reducing agent. As thereducing agent in chemical reactions, the α-alane may function as ahydride donor to reduce carbon-carbon double bonds or triple bonds or toreduce carbonyl moieties, such as ketones, aldehydes, carboxylic acids,esters, amides, and acid chlorides. The α-alane may also be used as apolymerization catalyst to catalyze addition polymerization reactions,such as the polymerization of olefin monomers or vinyl monomers.

To provide additional stability, the α-alane may be stabilized withpolyhydric monomers and polymers, such as aluminon (aurintricarboxylicacid triammonium salt), 8-hydroxyquinoline, or catechol.

EXAMPLES Example 1 Synthesis of α-alane (10 gram scale)

To a dry, 2-L roundbottom flask, 420 ml of anhydrous diethyl ether wasadded under an inert atmosphere and cooled to −10° C. Aluminumtrichloride (12.8 g) was added to the anhydrous diethyl ether, takingcare to not introduce moisture. A 1M LAH solution (440 ml) wastransferred to an addition funnel using a cannula and was added dropwiseto the solution of the aluminum trichloride in the diethyl ether. Thealuminum chloride and the LAH were reacted to form the alane-ethercomplex. The temperature of the reaction was controlled by adjusting therate at which the LAH solution was added. The temperature of thereaction was not allowed to rise above 0° C. When the reaction hadcooled down to from −8° C. to −10° C., 19 ml of diethyl ether was addedby syringe. The diethyl ether had been previously saturated with water.The resulting suspension was stirred for approximately 15 minutes. Thesuspension was then filtered through a Neutch filter, under an inertatmosphere, into a clean, dry container and was maintained at atemperature of below 0° C.

In a 12-L reactor having a dry addition funnel, a distillationapparatus, and a thermocouple, 5-L of anhydrous toluene was added underan inert atmosphere using a cannula. In addition, 3 ml of polydimethylsiloxane having a viscosity of 1 centistoke (“cSt”) and 100 mg of seedcrystals were added to the reactor. The solution of toluene,polydimethyl siloxane, and the seed crystals was heated to 92° C. Thesolution including the alane-etherate complex, produced as describedabove, was transferred to the addition funnel using a cannula and wasadded to the reactor. The addition of the alane-etherate complexsolution from the addition funnel was completed in approximately onehour, taking care that the rate of addition was not so rapid that thetemperature dropped below 88° C. The diethyl ether from thealane-etherate complex solution was removed by distillation andcollected in a 1-L addition funnel attached to a 1-L roundbottom flask.The reaction was continued for approximately 1 hour, until most of thediethyl ether was recovered.

The reaction was then cooled to 40° C. with a cooling bath.Approximately 500 ml of a 10% HCl solution was added very slowly to thereactor with a rapid nitrogen or argon purge. The HCl solution was addedat such a rate that the reaction did not foam out of the reactor. Whenall gas evolution had stopped, the resulting suspension was dischargedfrom the reactor into an Erlenmeyer flask and filtered on a glass frit.After filtering, the solid α-alane crystals were rinsed with water toremove the HCl. A rinse of acetone or isopropanol was used to remove thewater before drying the α-alane crystals.

Example 2 Effect of Borohydride Salts on the Production of α-alane

Experiments were conducted in which borohydride salts, such as lithiumborohydride or sodium borohydride, were used. The experiments showedthat the borohydride salts did not influence the course of the reactionbecause the reaction proceeded similarly in the absence and the presenceof the borohydride salts.

The experiments conducted in the absence of the borohydride saltsindicated that the borohydride salts are not necessary to produce theα-alane, which is contrary to the teachings of known methods ofproducing α-alane. By eliminating the need for the borohydride salts,the production of the α-alane is cheaper and generates fewer byproductsthat need to be disposed of.

Example 3 Synthesis of α-alane Utiziling a Mixed Solvent System andPolydimethylsiloxane

To a dry, sealed, 3-L, 3-neck roundbottom flask having an argon purgeand an overhead stirrer, 100.5 ml of anhydrous ether and 210 ml ofanhydrous toluene were added. Using an ice/acetone bath, the mixture wascooled to −10° C. With the argon purge across the open neck, 44.25 g ofaluminum chloride was added slowly enough that the temperature did notrise above 5° C. and no ether vapors were produced. In a separate, dry,sealed 2-L roundbottom flask equipped with an argon purge at ambienttemperature, 500 ml of 2.4M LAH in diethyl ether, 700 ml of anhydrousether, and 300 ml of anhydrous toluene were combined, respectively. Theice bath was removed from the aluminum chloride solution. Using acannula, the LAH mixture was transferred into the 3-L roundbottom flaskcontaining the aluminum chloride solution. Since the reaction wasexothermic, the temperature was maintained at approximately 20° C. withintermittent cooling as needed. The mixture was stirred for 10 minutesand then allowed to sit so that solids settled to the bottom.

In a dry, sealed 12-L jacketed reactor equipped with an overheadstirrer, an argon purge, and a distillation apparatus, 5 L of anhydroustoluene and 7.5 ml of polydimethylsiloxane (1 cSt) were added. Themixture was heated to 95° C. Using a dry siphon tube, the etheratesolution from the 3-L roundbottom flask was transferred into thereactor, below the surface of the toluene, leaving behind the solids inthe 3-L roundbottom flask. The alane precipitated immediately uponaddition, along with distillation of the ether. Approximately 85% of theether was distilled. The reaction was stirred for 1 hour or until enoughether was collected.

Upon completion of the crystallization, the reactor contents were cooledto 30° C.-35° C. To quench the reaction, a 10% HCl solution was addeddrop-wise at first with a liberal argon purge, keeping the temperaturebelow 50° C. At least 1 L of the 10% HCl solution was used to completethe quench. The mixture was stirred for 45-60 minutes at approximately35° C. before separating the aqueous layer (containing the α-alane) andthe organic layer. The aqueous layer was drained into a 4-L Erlenmeyerflask containing 1.5 L of ice water. The organic layer was disposed of.The solid was filtered and washed liberally with water, isopropylalcohol, and ether, respectively. The solid was dried under vacuum atroom temperature with a slight nitrogen purge. The reaction yieldedapproximately 25 g of α-alane as small cubic-shaped crystals.

Example 4 Synthesis of α-alane Utiziling a Mixed Solvent System, Water,and Polydimethylsiloxane

In a dry, sealed 250 ml 3-neck roundbottom flask equipped with an argonpurge and an overhead stirrer, 5 ml of anhydrous ether and 10.5 ml ofanhydrous toluene were added. Using an ice/acetone bath, the mixture wascooled to −10° C. With the argon purge across the open neck, 2.2 g ofaluminum chloride was added slowly enough that the temperature did notrise above 5° C. and no ether vapors were produced. In a separate, dry,sealed 100 ml flask with an argon purge at ambient temperature, 60 ml of1M LAH and 15 ml of anhydrous toluene were combined, respectively. Aftertransferring the LAH solution, 3.5 ml of diethyl ether previouslysaturated with water was added at room temperature. The ice bath wasremoved from the aluminum chloride solution. Using a cannula, the LAHsolution was transferred into the 250 ml roundbottom flask containingthe aluminum chloride solution. The reaction was exothermic and wasmaintained at approximately 20° C. with intermittent cooling as needed.The mixture was stirred for 10 minutes and then allowed to sit so thatsolids settled to the bottom.

In a dry, sealed 500 ml reactor equipped with an overhead stirrer, anargon purge, a silicon oil heating bath, and a distillation apparatus,250 ml of anhydrous toluene and 0.375 ml of polydimethylsiloxane (1 cSt)were added. The mixture was heated to 95° C. Using a dry siphon tube,the etherate solution from the 250 ml roundbottom flask was transferredinto the reactor, below the surface of the toluene, leaving behind thesolids in the 250 ml roundbottom flask. The alane precipitatedimmediately upon addition, along with distillation of the ether.Approximately 85% of the ether was distilled. The reaction was stirredfor 1 hour or until enough ether was collected.

Upon completion of the crystallization, the reactor contents were cooledto 30° C.-35° C. To quench the reaction, a 10% HCl solution was addeddrop-wise at first with a liberal argon purge, keeping the temperaturebelow 50° C. At least 25 ml of the 10% HCl solution was used to completethe quench. The mixture was stirred for 45-60 minutes at approximately35° C. before separating the aqueous layer (containing the α-alane) andthe organic layer. The aqueous layer was drained into an Erlenmeyerflask containing 50 ml ice water. The organic layer was disposed of. Thesolid was filtered and washed liberally with water, isopropyl alcohol,and ether, respectively. The solid was dried under vacuum at roomtemperature with a slight nitrogen purge. The reaction yielded 1.25 g ofα-alane. The α-alane prepared by this method produced larger crystalswith more of a hexagonal habit than the method not using the partiallyhydrolyzed alane-ether solution.

Example 5 Synthesis of α-alane Utiziling a Mixed Solvent System andPolydimethylsiloxane

The experimental conditions utilized in Example 4 were repeated, exceptthat the water was omitted from the process.

To a dry, sealed 250 ml 3-neck round bottom flask equipped with an argonpurge and an overhead stirrer, 6 ml of anhydrous ether and 2.8 ml ofanhydrous toluene were added. Using an ice/acetone bath, the mixture wascooled to −10° C. With the argon purge across the open neck, 2.66 g ofaluminum chloride was added slowly enough that the temperature did notrise above 5° C. and no ether vapors were produced. In a separate, dry,sealed 150 ml flask with an argon purge at ambient temperature, 72 ml 1Mof LAH and 30 ml of anhydrous toluene were combined, respectively. Theice bath was removed from the aluminum chloride solution. Using acannula, the LAH mixture was transferred into the 250 ml roundbottomflask containing the aluminum chloride solution. The reaction wasexothermic and was maintained at approximately 20° C. with intermittentcooling as needed. The mixture was stirred for 10 minutes and thenallowed to sit so that solids settled to the bottom.

In a dry, sealed 500 ml reactor equipped with an overhead stirrer, anargon purge, a silicon oil heating bath, and a distillation apparatus,250 ml of anhydrous toluene and 0.5 ml of polydimethylsiloxane (1 cSt)were added. The mixture was heated to 95° C. Using a dry siphon tube,the etherate solution from the 250 ml roundbottom flask was transferredinto the reactor, below the surface of the toluene, leaving behind thesolids in the 250 ml roundbottom flask. The alane precipitatedimmediately upon addition, along with distillation of the ether.Approximately 85% of the ether was distilled. The reaction was stirredfor 1 hour or until enough ether was collected.

Upon completion of the crystallization, the reactor contents were cooledto 30° C.-35° C. To quench the reaction, a 10% HCl solution was addeddrop-wise at first with a liberal argon purge, keeping the temperaturebelow 50° C. At least 25 ml of the 10% HCl solution was used to completethe quench. The mixture was stirred for 45-60 minutes at approximately35° C. before separating the aqueous layer (containing the α-alane) andthe organic layer. The aqueous layer was drained into an Erlenmeyerflask containing 50 ml of ice water. The organic layer was disposed of.The solid was filtered and washed liberally with water, isopropylalcohol, and ether, respectively. The solid was dried under vacuum atroom temperature with a slight nitrogen purge. The reaction yielded 1.23g of α-alane as small (about 10 micron diameter) cubic crystals.

While the invention may be susceptible to various modifications andalternative forms, specific embodiments have been described in detailherein. However, it should be understood that the invention is notintended to be limited to the particular forms disclosed. Rather, theinvention is to cover all modifications, equivalents, and alternativesfalling within the spirit and scope of the invention as defined by thefollowing appended claims.

1. A method of producing α-alane, comprising: reacting aluminumtrichloride and an alkali metal hydride to form an alane-ether complexsolution; adding an aqueous ether solution to the alane-ether complexsolution to form a partially hydrolyzed ether/alane-ether complexsolution; adding a solution that comprises at least one crystallizationadditive to the partially hydrolyzed ether/alane-ether complex solutionto form a crystallization solution; and crystallizing α-alane from thecrystallization solution.
 2. The method of claim 1, wherein reacting thealuminum trichloride and the alkali metal hydride to form thealane-ether complex solution comprises reacting the aluminum trichlorideand the alkali metal hydride in diethyl ether or in a mixed solventsystem comprising greater than approximately 50% diethyl ether.
 3. Themethod of claim 1, wherein reacting the aluminum trichloride and thealkali metal hydride to form the alane-ether complex solution comprisesreacting an alkali metal hydride selected from the group consisting oflithium hydride, sodium hydride, potassium hydride, calcium hydride,magnesium hydride, lithium aluminum hydride, sodium aluminum hydride,and mixtures thereof with the aluminum trichloride.
 4. The method ofclaim 1, wherein adding the aqueous ether solution to the alane-ethercomplex solution to form the partially hydrolyzed ether/alane-ethercomplex solution comprises adding an aqueous ether solution comprisingfrom approximately 0.5% by volume to approximately 4% by volume of waterto the alane-ether complex solution.
 5. The method of claim 1, whereinadding the solution that comprises at least one crystallization additiveto the partially hydrolyzed ether/alane-ether complex solution to formthe crystallization solution comprises adding the partially hydrolyzedether/alane-ether complex solution to the at least one crystallizationadditive dissolved in toluene.
 6. The method of claim 1, wherein addingthe solution that comprises at least one crystallization additive to thepartially hydrolyzed ether/alane-ether complex solution to form thecrystallization solution comprises combining the partially hydrolyzedether/alane-ether complex solution with a solution that comprises the atleast one crystallization additive selected from the group consisting ofsqualene, cyclododecatriene, norbomylene, norbornadiene, a phenylterminated polybutadiene, 2,4-dimethyl anisole, 3,5-dimethyl anisole,2,6-dimethyl anisole, polydimethyl siloxane, and mixtures thereof. 7.The method of claim 1, wherein adding the solution that comprises atleast one crystallization additive to the partially hydrolyzedether/alane-ether complex solution to form the crystallization solutioncomprises formulating the crystallization solution to be free of analkali metal borohydride.
 8. The method of claim 1, whereincrystallizing the α-alane from the crystallization solution comprisesremoving ether from the crystallization solution.
 9. The method of claim1, wherein crystallizing the α-alane from the crystallization solutioncomprises heating the crystallization solution to a temperature rangingfrom approximately 80° C. to approximately 97° C. to reduce a volume ofether in the crystallization solution to less than approximately 10% byvolume.
 10. The method of claim 9, further comprising adding additionalether to the crystallization solution after reducing the volume of etherin the crystallization solution to less than approximately 10% by volumeand heating the additional ether and the crystallization solution to atemperature ranging from approximately 88° C. to approximately 95° C. toproduce the α-alane.
 11. The method of claim 1, further comprisingexposing the α-alane to an acidic solution comprising from approximately10% by volume to approximately 12% by volume of hydrochloric acid.
 12. Amethod of producing α-alane, comprising: reacting aluminum trichlorideand an alkali metal hydride to form an alane-ether complex solution;adding an aqueous ether solution to the alane-ether complex solution toform a partially hydrolyzed ether/alane-ether complex solution; adding asolution that comprises at least one crystallization additive to thepartially hydrolyzed ether/alane-ether complex solution to form acrystallization solution, wherein the crystallization solution is freeof an alkali metal borohydride; and crystallizing α-alane from thecrystallization solution.
 13. A method of producing α-alane, comprising:reacting aluminum trichloride and an alkali metal hydride to form analane-ether complex solution; combining the alane-ether complex solutionwith a solution that comprises at least one crystallization additive toform a crystallization solution, wherein the at least onecrystallization additive is selected from the group consisting ofsqualene, cyclododecatriene, norbomylene, norbomadiene, polydimethylsiloxane, and mixtures thereof; and crystallizing α-alane from thecrystallization solution.
 14. The method of claim 13, wherein reactingthe aluminum trichloride and the alkali metal hydride to form thealane-ether complex solution comprises reacting an aluminum trichlorideand the alkali metal hydride in diethyl ether or in a mixed solventsystem comprising greater than approximately 50% diethyl ether.
 15. Themethod of claim 13, wherein reacting the aluminum trichloride and thealkali metal hydride to form the alane-ether complex solution comprisesreacting the alkali metal hydride selected from the group consisting oflithium hydride, sodium hydride, potassium hydride, calcium hydride,magnesium hydride, lithium aluminum hydride, sodium aluminum hydride,and mixtures thereof with the aluminum trichloride.
 16. The method ofclaim 13, wherein combining the alane-ether complex solution with thesolution that comprises the at least one crystallization additive toform the crystallization solution comprises combining the alane-ethercomplex solution with a solution that comprises from approximately 0.05%by weight to approximately 5% by weight of the at least onecrystallization additive.
 17. The method of claim 13, wherein combiningthe alane-ether complex solution with the solution that comprises the atleast one crystallization additive to form the crystallization solutioncomprises combining the alane-ether complex solution with the at leastone crystallization additive dissolved in toluene.
 18. The method ofclaim 13, wherein combining the alane-ether complex solution with thesolution that comprises the at least one crystallization additive toform the crystallization solution comprises formulating thecrystallization solution to be free of an alkali metal borohydride. 19.The method of claim 13, wherein crystallizing the α-alane from thecrystallization solution comprises removing ether from thecrystallization solution.
 20. The method of claim 13, whereincrystallizing the α-alane from the crystallization solution comprisesheating the crystallization solution to a temperature ranging fromapproximately 80° C. to approximately 97° C. to reduce a volume of etherin the crystallization solution to less than approximately 10% byvolume.
 21. The method of claim 20, further comprising adding additionalether to the crystallization solution after reducing the volume of etherin the crystallization solution to less than approximately 10% by volumeand heating the additional ether and the crystallization solution to atemperature ranging from approximately 88° C. to approximately 95° C. toproduce the α-alane.
 22. The method of claim 13, further comprisingexposing the α-alane to an acidic solution comprising from approximately10% by volume to approximately 12% by volume of hydrochloric acid.